The invention relates to a method for preparing alkali and heat stable polyols, in which sugar alcohols are treated with reagents to obtain a stabilized sugar alcohol syrup by means of reagents and the stabilized alcohol syrup is subjected to a purification stage by passing the stabilized sugar alcohol syrup over at least one ion-exchanger resin.
By polyols are meant sugar alcohol syrups, by which reference is made to the hydrogenation products of polysaccharide hydrolysates, comprising, but not restricted to, hydrolysates obtained from starch, xylanes, arabinoxylanes, cellulose or other vegetal polysaccharides. Typical starch hydrolysates are, for instance, dextrose, high DE glucose syrups, high maltose syrups, standard glucose syrups and maltodextrines, including low DE maltodextrines.
Alkali and heat stability or sugar alcohols is important in a number of industrial and food applications, as shown in JP 63/079644 and EP 0 711 743. The alkali and heat stability in these patent documents is obtained by treating sugar alcohols by means of reagents in such a manner that as much colour forming components as possible are removed.
In JP 63/079844 sugar alcohol syrups are treated at a pH=9.5–13 at high temperatures and during a period varying between 30 minutes and 2 hours.
In EP 0 711 743 stabilization is realized through a fermentation, oxidation or caramelisation stage.
The thus stabilized sugar alcohol syrup is then further subjected to a purification stage in order to obtain the final product.
In JP 63/079844 this purification stage comprises a treatment of the treated syrup with ion exchanger resins. Here the syrup, which was cooled down to 50° C. was first passed over a strong acid cationic resin, then over a weak or medium base anionic resin and finally over a mixed bed, composed of the same cationic and anionic resins as mentioned above and in a 1:2-ratio. The temperature at which these resins were used not being mentioned in this patent document.
In example 1 of EP 0 711 743, the stabilized syrup is purified by means of a strong acidic cationic resin and a strong basic anionic resin. Here also, no reference is made to any temperature at which these ion exchange resins are used.
In EP 1 095 925 an improved method is considered for purifying sugar alcohol syrups which were subjected to an alkali and heat stabilization treatment. In this method purification occurs by at least one passage of the stabilised sugar alcohol syrup over a strong acidic cationic resin at a temperature of below 50° C., in a preferred form of below 40° C. and in the most preferred form the temperature is situated between 20° C. and 30° C.
In EP 1 095 925 the importance of the working temperatures of resins with respect to the level of reducing sugars desired after purification is mentioned. From this it is apparent that working temperatures of below 30° C. give cause for products having an excellent heat and alkali stability, such as required for a number of applications.
The temperature is the more important when the hydrolysable sugar alcohol content of the syrup, for instance, maltitol, maltotriitol and hydrogenated oligosaccharides, increases.
From U.S. Pat. No. 5,254,174 the importance of the working temperature of strong acidic cationic resins with respect to the hydrolysis of the substrate treated, is considered. There, with respect to the oligosaccharide treatment, it is suggested to use the strong acidic cationic resins at temperatures situated between 25° C. and 35° C., in order to prevent hydrolysis of the oligosaccharides.
In U.S. Pat. No. 4,029,183 is considered how the inversion reaction of sucrose during decationization, is prevented by controlling the temperature of the strong acidic cationic resin between 25° C. and 30° C.
The use of strong acidic cationic resins during the refining of stabilised sugar alcohol syrups, however, has the disadvantage that, when products having a low reducing sugar content are needed, it is necessary to work at temperatures between 20° C. and 30° C. In order to cool down the syrups to these relatively low temperatures, additional cooling equipment and energy has to be used. As a consequence of these lower temperatures, the viscosity of these relatively concentrated syrups increases, because of which treatment is further complicated (pressure build-up in resins). This is more especially the case with syrups obtained through hydrogenation of, among others, starch hydrolysates that are mainly composed of di-, tri- and higher oligosaccharides (for instance, medium and high maltose syrups, maltodextrines). Another disadvantage of strong acidic resins is related to the fact that a large excess of acid is required in order to regenerate these resins.
In EP 0 262 711 the use of a combination of weak acidic cationic and weak or medium basic anionic resin is considered for purification of beet sugar thin juice.
It should be noted that this method aims at a partial demineralisation of beet sugar thin juice (as described in the examples). However, from these examples it becomes clear that the removal of cations and colour is far from complete.